The present invention relates generally to an electronic timepiece, and in particular to controlling the display of an analog electronic timepiece.
It is known to control the sweep hand of an analog electronic timepiece as disclosed in U.S. Pat. No. 3,961,213. Reference is made to FIG. 1 wherein such a conventional timepiece is provided. The intermittent rotational energy of an actuator is stored by the attractive magnetic forces of a drive magnet 51. Drive magnet 51 is coupled to a fourth wheel and pinion 59 which is supported on a gear plate 60 by one end of its axis 58. Within a bridge 56 supporting the other end of axis 58, a cavity 61 sealed by cap 55 contains a viscous fluid 54. A driven magnet 53 is immersed in the viscous fluid 54 and is magnetically coupled to drive magnet 51. Driven magnet 53 rotates smoothly due to the viscous resistance between bridge 56 and driven magnet 53 provided by viscous fluid 54.
A second hand shaft 57 is freely rotatably mounted in a conventional manner. A follower magnet 52 is mounted on one end of second hand shaft 57 and magnetically interlocks with driven magnet 53 to smoothly rotate second hand shaft 57.
The prior art electronic timepiece has been satisfactory. However, because the viscous resistance of viscous fluid 54 varies with temperature, the time indicated by the second hand will also deviate with temperature because of a change in the relationship of the viscous resistance and the attractive force of the magnets. As the temperature decreases the viscous resistance becomes too large with respect to the magnetic attractive force. Additionally, it has been noticed that it is difficult to completely seal the fluid so that fluid leakage occurs, changing the characteristics of the sweep hand. Because the rotational characteristics of the shaft and hand are determined by the attractive forces of magnet 52 and the viscous resistance of fluid 54, there is a wide range of variety in performance of the sweep hand among the different manufactured products which is extremely difficult to adjust to provide a uniform sweep hand characteristic.
Accordingly, it is desirable to provide a control for the display in an electronic timepiece which overcomes the shortcomings of the prior art devices described.